ABSTRACT Despite recent advancements, metastatic pancreatic cancer remains a lethal disease with an average survival of less than one year. New targeted treatments are desperately needed. Identifying and expanding patient subgroups that would benefit most from promising targeted agents will immediately impact patient outcomes. The primary impact of our proposal relates to the clinical implementation of PARP inhibitors, harnessing a proven synthetic lethal therapeutic strategy personalized for a subset of pancreatic cancer patients. Recent whole genome sequencing of 100 pancreatic cancers highlighted the opportunity to use PARP inhibitor therapy targeted for tumors with a `DNA repair-BRCA-signature' subtype. Our work will expand three fronts of investigation and innovation in an effort to optimize the most promising drug class for pancreatic ductal adenocarcinoma patients. Aim 1 will expand our recent discovery that a post- transcriptional mechanism driven by the mRNA stability factor HuR, provides a resistance mechanism for pancreatic cancer cells exposed to PARP inhibitors. In this aim, we will extend our pre-clinical mouse modeling to establish HuR as a facilitator of PARP inhibitor resistance and establish that inhibiting HuR may sensitize all pancreatic tumors, regardless of DNA repair status, to PARP inhibitors. Aim 2 will further define, using cutting edge molecular and cell-based techniques and assays, a PARP inhibitor mechanism of action which is contingent upon a novel HuR-regulated target [i.e., (Poly(ADP-ribose) glycohydrolase (PARG)]. Aim 3 will leverage our molecular understanding of HuR biology and the identification of two small molecule inhibitors of HuR to develop novel and translatable strategies to enhance PARP inhibitor efficacy using a patient derived (i.e., organoid technology), live biobank from an ongoing PARP inhibitor trial conducted by investigators from the present proposal. The translational significance of our work relates to our efforts to improve upon a promising, personalized approach to pancreatic cancer through increased understanding of a recently discovered PARP inhibitor resistance mechanism. Our ultimate aim is to optimize a best-in-class treatment strategy presently limited to tumors harboring DNA repair deficiencies, so that this therapeutic strategy may be extended to include all pancreatic cancers, regardless of the DNA-repair status (i.e., BRCA2 mutant and wild type).